Guest Post: presenting Diabloceratops eatoni

Dr. James Kirkland (L), and Paleontologist Don Bileux (R) who discovered the skull, answer questions about the Ceratopsian skull from children from the Cosgriff Catholic School. Scott Sommerdorf / The Salt Lake Tribune

This newly named ceratopsian dinosaur, based on a superbly preserved and amazing looking skull has already been doing the rounds in the media and on various blogs. Lead author Jim Kirkland has been good enough to pen this guest post on the discovery of the specimen and its importance in terms of the evolution of the group and the characters of the skull within the clade.

Well, on May 28thDiabloceratops eatoni became a part of the ceratopsian pantheon with the publication of “New Perspectives on Horned Dinosaurs: The Royal Tyrell Museum Ceratopsian Symposium” only two and a half years after the symposium. The road was long; Don DeBileux found the skull in 2002 as part of a paleontological inventory we (Utah Geological Survey) were conducting of the middle Campanian Wahweap Formation for the Grand Staircase – Escalante National Monument (GSENM) in southern Utah. Don and many volunteers from Utah Friends of Paleontology spent many long hours rock sawing the skull out of the hard sandstone. It sat for several years until GSENM paleontologist Alan Titus secured free helicopter transportation to get the skull block to the road. Don then spent over 800 hours freeing the beautiful skull from the sandstone. The skull was beautiful and undistorted, but much of the right side was missing, although all aspects of the skull were represented. This was followed by Rob Gaston of Gastondesign doing his usual skilled job molding and reconstructing the missing elements to construct a full reconstruction of the skull. Given opportunities to study all the other North American ceratopsian skulls and thanks to my friend Hailu You made several trips to China, I was able to fully appreciate the distribution of character states in this clade and place it in its proper phylogenetic context and there lies the importance of this specimen.

Diabloceratops. Image courtesy Jim Kirkland.

Sure, for the moment, it is the oldest known ceratopsid, sure it is spectacularly ornamented, sure it is the first centrosaurine described south of Montana, and sure it is clearly a basal centrosaurine based on the presence of the derived stepped-squamosal and nasal-premaxillary process and in having long brow-horns as in the ceratopsid sister taxon Zuniceratops. But Diabloceratops also has a well-developed character, whose significance had not been realized before this discovery. It possessed a well-developed opening at the contact of the nasal, premaxilla, and maxilla forward of the antorbital fenestra that we call the accessory antorbital fenestra (AAF). Following examination of the distribution of this distinct character much was revealed regarding the origin and radiation of the ceratopsids.

Diabloceratops head on. Image courtesy Jim Kirkland.

Diabloceratops skull, rear view. Image courtesy Jim Kirkland.

First, among more basal neoceratopsians (i.e. “protoceratopsids”), only Magnirostris and Bagaceratops share this distinct character. Protoceratops itself has a well-developed fossa in this position, but there is no opening. The sole specimen of Hailu You and Dong Zhiming’s (2003) Magnirostris dodsoni at the IVPP has a well-preserved AAF of virtually the exact morphology as that in Diabloceratops. Additionally, Magnirostris possesses tiny orbital horns. Thus, the distribution of this character in the Asian “protoceratopsian grade” neoceratopsians eliminates the last hope of preserving a distinct clade for Protoceratops and its closest sister taxa. The resulting phylogenetic scenario indicates that Protoceratops, Bagaceratops, Magnirostris, represent a progression of taxa with increasing affinities to the ceratopsids.

Our own Zuniceratops, with its distinct mosaic of primitive and derived characters, is well accepted as a more derived sister taxon to the ceratopsids, but as it is represented by disarticulated skulls; initial reconstructions suggested that it possessed a distinctly enlarged antorbital fenestra. Reexamination indicates that it possessed an AAF like that of Diabloceratops.

Also of some significance is the distribution of the AAF in the more derived ceratopsids. It is not known in more derived centrosaurines, but a reduced AAF between the maxilla and nasal is present in specimens of Chasmosaurus with large brow horns, suggesting a reappraisal of the species of Chasmosaurus is needed, and in the southern chasmosaurines Pentaceratops and Aguaceratops. Therefore, given the various evolutionary scenarios floating around for ceratopsids, it would appear that the AAF was lost in at least 3 times in the Ceratopsia. Rigorous studies phylogenetic studies of ceratopsians are under way and we will see how our phylogenetic hypothesis holds up.

Given that our hypothesis of the phylogenetic significance of the AAF holds up under further scrutiny, why would something that was surely of adaptive significance in the derived “protoceratopsian grade” neoceratopsians be repeatedly lost in the Ceratatopsidae? Our hypothesis for this is simple given our acceptance of Scott Sampson’s hypothesis that ceratopsid horns were used in intraspecific combat; i.e. wrestling matches. Such combat would put severe strain on the skull of these horn-bearing ceratopsids and lead to selective pressures to strengthen the skull and the subsequent loss of the AAF. Thus, it was good at the time, but on second thoughts…..

Our take home message, to be tested by the paleontological hordes that follow, is that the identification of a significant new character can actually be more important than describing a new dinosaur, no matter how cool it is.

Witmer, L. M. 1997. The evolution of the antorbital cavity of archosaurs: A study of soft tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. Society of Vertebrate Paleontology Memoir 3: 1-73.

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25 Responses to “Guest Post: presenting Diabloceratops eatoni”

Er… saying “the distribution of this character in the Asian “protoceratopsian grade” neoceratopsians eliminates the last hope of preserving a distinct clade for Protoceratops and its closest sister taxa” is unwarranted. I have no opinion on ceratopsian phylogenetics, but surely if it was lost three times in ceratopsids, it could have been lost in Protoceratops as well. Again, I don’t necessarily think it was lost in Protoceratops, but a single character can never completely disprove any topology. I do agree with the take home message though, as I also often find characters to be more interesting than taxa.

The Ceratopsidae just get more and more interesting. As far as ceratopsian phylogenetics go I agree with Kirkland that more studies need to be done on Chasmosaurus, for example should Agjuaceratops be considerd in the Chsamosaurus genera again rather than it’s own species?
It also seems like now that centrosaurines are now being found with longer brow horns (Diabloceratops and Albertaceratops) being the prime examples. Where before long brow horns were more common in chasmosaurines. Maybe these new finds should also help redefine which characters seperate centrosaurinae from chasmosaurinae.
Lastly, 2009 seems to have produced a lot of new research in general on the ceratopsidae. With all the centrosaurines being found and the ontogeny on Triceratops, with the possiblity of Triceratops and Torosaurus being the same kind of animal. It looks like there is lot of new research on the horizon for ceratopsians.

I don’t know if it’s just me but with all these new forms announced up in the last week or so, im finding it very difficult to see the morphological distinction between the primitive/stratigraphically older centrosaurine & chasmosaurine skulls (eg. Sinoceratops & Diabloceratops). Given the superficial similarity between Albertaceratops & Medusaceratops yet them being unrelated (but relatively close to centrosaurine-chasmosaurine node), i’m wondering what Coahuilaceratops will clade together with.

I have a question regarding modern practises in the reconstruction of fossils. It used to be that reconstructed parts in fossil skeletons were clearly differentiated from the actual fossil. You could usually see clear diferences in color and texture between what was real and what was based on conjecture. It seems far more comon these days to have highly detailed models, such that it seems impossible to determine where the original fossil ends and the reconstruction begins. Why has this practice become so widespread? Personally, I find it quite annoying, and I worry that it may come to undermine the percieved credibility of palaeontology (especially among those who aren’t too clear on the science in the first place) if folks aren’t up front about what exactly has been discovered, and what has been filled in based on other specimens.

Jeepers, that ended up long-winded. Hope you found my question in there.

I think it’s a combination of wanting the stuff to look nice (i.e. complete) and the public always wanting to know what it looked like. While obviously a mix of finished and unfinished material can show the complete reconstruction while filling in the gaps, the public does, oddly to my mind, not seem to find it satisfying.

I don’t think it does undermine the credibility of the subject though since a) it happens a lot and many specimens are chimeras, or casts, or composites etc. and have been for a very long time, and b) most places include photos of the original material, or blocked out figures to show what was found etc. or simply describe it in the signs / guidebooks.

Most importantly, the scientists are always clear and open about this in the research papers. While obviously that doesn’t always reach the public, they don’t have to dig far to find out. I think most people do know that most dinosaurs are not found complete and articulated and in beautiful condition, and if they don’t they either don’t care or will find out pretty quickly.

What an astonishing looking animal. It looks like someone hit the stop button half way through a morph between Triceratops and Styracosaurus.
Are we running out of horn and frill configurations for ceratopsians yet?

The frill is very strange in this new animal. It is almost triangular in anterior view, pointing up. In some chasmosaurines (particularly Chasmosaurus), the frill is triangular, but the flat end is up in anterior view. The parietals are also surprisingly narrow.

I do wonder about reconstructions I’ve seen that give Diabloceratops a nasal horn, though. I wouldn’t say that the nasal has a horn as much as a rugose surface. Given the tall nose, I’d suggest that it simply had a small boss running along the top of the nasals. Maybe?

Yeh, I probably understated it in the quick painting I did, but I’d be surprised to see a horn on such a narrow area of bone.

It has a quite conical shape that would lend itself to a nice horn like bump though.

The prominent horns at the back of the frill appear to have a real distinction between where the flesh of the head ends and the keratin sheath begins. It’s not something I’ve noticed before in ceratopsian skulls.

Gahhhhd thats a cool looking ceratopsian! What a perfect (and memorable) name for it too! Every 9 year old who’s favourite dinosaur has always been triceratops or styracosaurus is gonna be seriously reconsidering when they learn about this monster. I anticipate a lot of “wellll, I have two favourites now…”

WHAT SIZE OF THIS DIABLOCERATOPS SKULL BONE?
HOW I DO NOT HOW bores LENGTH OF SKULL BONE DIABLOCERATOPS LENGTH AND HEIGHT? ONLY HEAD DIABLOCERATOPS? AND PLEASE REPLY ME AND SEND MY E-MAIL: HUG EPILEF_AMIL_1979@HOTMAIL.COM OK THANKS REPLY

the new ceratopsian is awesome and i know you’ve named it diabloceratops because of it’s two huge horns on it’s frill, but the name diablo is also means evil spirit. let’s be honest it’s not evil-looking, is it?